HVLP technology has developed in two ways as mentioned above. The first and easiest adaptation was changing the gun design while continuing to use the standard compressed piston air system. Here the standard piston type pump pushes air into a storage tank which is connected directly to the paint gun and used on demand. Pressures from the tank can be 30 to 100 PSI (depending on where the tank pressure is set) which is then reduced to HVLP pressures of less than 10 PSI inside the spray gun. This type of system is know as Standard HVLP where the gun is designed to release a controlled amount of compressed air into a larger chamber that expands to create the air volume needed for HVLP application. U.S. Pat. No. 5,429,307 details such a design where a gun has been designed to accept either type of air source, compressed air from conventional piston pumps or HVLP air from a turbine pump, by means of a simple adjustment on the gun. Air volume for True HVLP systems is produced directly by turbine type pumps with guns designed to operate at the lower pressures. True HVLP guns are designed to have large passageways to accept the lower pressure from the HVLP turbine and propel the coating at almost the same pressure as it received minus air losses within the gun. The Standard HVLP compressors have high pressure but lack the volume necessary to atomize the coating whereas the True HVLP turbine has the necessary volume required for light atomizing but many times lacks the pressure to deliver the coating at 10 PSI, the maximum permitted by HVLP regulations. Standard HVLP is not as efficient as True HVLP and can typically achieve 55-65% maximum transfer efficiency while the True HVLP systems with stacked Turbines and True HVLP guns have achieved 70 to 80% transfer efficiencies and are therefore the preferred method of HVLP. An additional advantage that True HVLP systems have over the Standard HVLP is that the Standard piston type pumps that have rings and seals that often leak exhaust particles, water and lubricating oil. The air they pump cannot be used for atomizing coatings or for fresh air breathing without adding costly filters and regular maintenance. The True HVLP turbine pumps are oil less, and keep the air stream clean and free from contaminates so atomized coatings are particle and pollution free without such cost and maintenance.
Since the 1980's when HVLP technology became accepted as a viable alternative to convention spray systems, manufactures have developed turbine style motors like those found in vacuum cleaners that can be stacked to achieve larger amounts of pressure at the output. A typical flat or “pancake” style turbine can produce 20 CFM of air volume but only 2-3 PSI of output pressure. So HVLP manufactures began stacking the turbines in series to produce more air pressure and approximate the 10 PSI maximum allowed by HVLP protocol. Unfortunately stacking these individual turbine elements creates inherent heat and inefficiencies and the practical maximum any manufacturer has been able to achieve to date in output pressure is around 7 PSI, or 30% below the allowable and optimum HVLP pressure allowed. Not having the maximum 10 PSI allowed at the Spray gun tip limits the amount of coating that can be applied per hour (or throughput) so even though transfer efficiency is increased so is the application times leading to higher coating costs.
The secret to producing a good quality finish is finding a balance between atomizing pressure and fluid viscosity. When both are properly matched it will create good atomization of the coating and steady delivery of atomized coating suspended in air, producing a smooth, even and consistent finish when dry. Unfortunately, most present day HVLP systems are able to atomize only low solid coating formulations so their application and value is limited to only a small part of the coating business. The present invention details using a rotary vane HVLP turbine, as opposed to conventional “pancake” or stacked type HVLP turbine and has the advantage of being able to produce an excess volume of air which can be used to atomize high solid coating formulations, power multiple guns and simultaneously and provide a fresh air breathing system for the spray operators. The stacked pancake style HVLP turbine is limited in volume and therefore no extra air is available to supply breathing systems. The rotary vane pump of present invention has a clear advantage in output capacity but is expensive in comparison. So the present invention also provides a means to overcome the cost disadvantage of the rotary vane pump as applied to HVLP coatings applications by means of a manifold that allows one pump to supply multiple guns as well as a fresh air breathing system for the spray operator. By utilizing a rotary vane pump in place of the conventional stacked turbine the present invention has been able to achieve 10 to 16 PSI of pressure to allow for losses within the system so that the final output at the spray gun cap can be 10 PSI which meets the optimum operating conditions of HVLP operation. The use of the rotary vane pump in the present design also allows 50-70 CFM of output volume, for atomizing high solid coatings, supplying multiple HVLP guns and providing fresh air for controlled operator breathing through air mask assemblies. Current true HVLP technologies all utilize stacked style turbine motors because they are relatively inexpensive and inherently efficient. They have the disadvantages of having a short operational life and are noisy, but their greatest limitation is not having the capability to deliver the necessary 10 PSI air pressure required for most industrial HVLP applications and having enough volume to atomize high solid coatings. Another disadvantage is that they heat the air that is compressed causing heat curing, a premature chemical reaction within the coating as it is applied which affects the finish. The present invention overcomes all these limitations.
Due to the concern for VOC pollution, more coating producers are formulating their coatings with higher solid content, which helps limit VOC emissions but requires extra volumes of air to atomize. Convention HVLP turbines do not have the capacity to atomize many of these formulations. Because of these and other technical drawbacks, the HVLP field of coating applications today has been restricted to smaller project painting of limited sized objects with coatings of low solid content (easy to atomize). One popular HVLP application today is use in furniture spraying where small items such as chairs and tables are sprayed with lightweight materials like lacquer and clear enamel with delivery rates and production times that are not cost critical. The throughput of the current HVLP paint systems or the amount of paint that can be delivered per a given timeframe is small compared to other Systems so for many coating applications, HVLP has no practical or economical use despite the fact that it has much higher transfer efficiency. The present invention is designed to overcome the pressure delivery and atomization problems of the stacked turbine HVLP technology by providing a pump powered by a rotary vane turbine that is not limited in delivery pressure or atomizing volume. This excess pressure and volume capacity fit the HVLP model well since it can now deliver the maximum HVLP output pressures of 10 PSI at the spray gun cap or output with enough excess pressure to accommodate system losses, while its ability to generate large volumes of air, as compared to conventional HVLP stacked turbines allow it to atomize high solid coatings with ease. The added volume capacity along with the unique manifold design of the present invention allows the rotary vane pump to supply multiple spray gun outputs, increasing coating efficiency and lowering application costs. This added volume can also be used to supply a fresh air breathing and cooling apparatus for the spray gun operator. Fresh air for coating operators is a critical requirement where large amounts of coatings are sprayed in a closed or restricted space area such as an airplane hanger or a military maintenance depot or where toxic coatings are being used such as CARC, chemical agent reactive coatings. Current technology requires spray operators to carry their own air supply in these situations which consists of tanks strapped on their backs, limiting range and motion of the operator as well as causing operator fatigue. The present invention overcomes the problems by supplying fresh filtered air into a sealed mask at each spray station which can be individually adjusted by the operator. Air from the rotary vane pump is clean, there is no oil or water as there is with conventional piston pumps so the need for external air filtering is minimized. All this is accomplished from a single output manifold without the need for oxygen storage tanks, filters or elaborate breathing systems that hinder the efficiency and increase the costs of coating process. The present invention provides a break through design for the HVLP market because all previously mentioned limitations of HVLP spray technology are now eliminated. HVLP Spraying can now be applied to large scale coating targets with increased coating atomization, delivery speed and delivery performance. Coatings can be produced that are more even, contain less air bubbles, pits and other surface imperfections, all while creating less overspray and coating waste. Having the multiple spray stations possible from one pump source increases coating productivity and efficiency by orders of magnitude and having a fresh air source for operator breathing allows the system more versatility and range of applications never possible with previous HVLP designs.
The present design also has a coating supply system that is central and independently pressurized, which directly supplies each gun via a hose reducing the down time of the spray coating process. Typically, most HVLP spray systems utilize a gun that contains a cup reservoir that must be re-filled many times during the operation, causing time consuming delays and labor inefficiencies. The present design eliminates the need for a spray gun cup reservoir and supplies the coating direct via hose under operator adjustable pressure greatly increasing coating delivery efficiency and performance saving labor costs.